1. Field of the Invention
The present invention is related to a machine tool.
2. Background Art
A machine tool comprising a frame-like machine rack in which an x skid runs horizontally displaceable on guides is known from EP 0 742 072. Inside the x skid, another y skid runs vertically displaceable on guides. For actuation, x linear motors and y linear motors are provided which are arranged with their sides facing each other so that the forces of the x linear motors acting in y direction and the forces of the y linear motors acting in x direction cancel each other out, providing a symmetry of forces. The same applies to the drives of a z skid which carries a tool spindle and which rests on the y skid. This so-called box-in-box construction is widely used because of the compact and rigid framework construction and the symmetry of forces. As a disadvantage, the working of the skids and the assembly and, if necessary, maintenance work are complicated due to the difficult accessibility of the guides and linear motors. Because of the symmetry of forces, the guides are essentially not biased so that the wear of the guides causes a backlash of the guides, which affects the processing quality.
A similar embodiment is known from U.S. Pat. No. 5,688,084 A.
U.S. Pat. No. 6,012,884 A describes a machine tool comprising a frame-like rack with an x skid provided thereon which is horizontally displaceable in the x direction and on which a y skid is vertically displaceable in the y direction. Inside the y skid, a z skid is arranged, carrying a tool spindle. An x linear motor arranged in the region of a lower x guide is provided to drive the x skid. Two y linear motors facing each other symmetrically and acting by force balance are provided to drive the y skid.
It is an object of the present invention to embody a machine tool which comprises an x skid and a y skid displaceably arranged thereon, with the latter carrying a tool spindle, and the skids of which can be manufactured at a low manufacturing expense and then easily be assembled, and which are free of any guide backlash irrespective of the wear of the guides.
According to the present invention, this object is achieved in a machine tool comprising a frame-like rack defining an inner space, and having a front side positioned in an x-y plane; an x skid having a- rear side facing the front side, and a face side turned away from the rear side and assigned to an operating side; x guides mounted on the rack on the one hand, and on the x skid on the other, and allowing a displacement of the x skid relative to the rack in x direction; y guides mounted on the x skid on the one hand, and on the y skid on the other, and allowing a displacement of the y skid relative to the x skid in y direction; a tool spindle arranged in the y skid and extending in z direction; x linear motors arranged on the front side of the rack on the one hand and on the rear side of the x skid on the other, each comprising a primary part and a secondary part, and each comprising an air gap between the primary part and the secondary part, wherein the air gaps of the x linear motors are arranged in a common x-y plane; and y linear motors arranged on the face side of the x skid on the one hand and on the rear side of the y skid on the other, each comprising a primary part and a secondary part, and each comprising an air gap between the primary part and the secondary part, wherein the air gaps of the y linear motors are arranged in a common x-y plane. Due to the design according to the present invention, manufacturing the rack and the x skid and the y skid in the vicinity of the respective linear motors is very simple, as only freely accessible front sides have to be worked. Also, the assembly is very simple, as the assembly surfaces are freely accessible. Further, the specific arrangement of the linear motors ensures that the forces of attraction that act in linear motors transversely to the direction of motion act only in the z direction, thus compensating for any guide backlash in the guides. Even when a backlash occurs due to wear of the guides, the guides can normally still be used while they have to be replaced in the conventional construction of the prior art.
The characteristics which consist in that the x guides are attached to the front side of the rack on the one hand and to the rear side of the x skid on the other, and in that the y guides are attached to the face side of the x skid on the one hand and to the rear side of the y skid on the other, ensure that also the assembly surfaces of the guides can be worked very easily and the guides themselves can be assembled with little expense. Further, each individual guide is loaded symmetrically in this construction.
When a first part of each x linear motor is arranged on the front side of the rack and a second part is arranged on the rear side of the x skid; when a first part of each y linear motor is arranged on the face side of the x skid and a second part is arranged on the rear side of the y skid; when the x guides are mounted on the rack and the x skid, respectively, by screws that extend in z direction; and when the y guides are mounted on the x skid and the y skid, respectively, by screws that extend in z direction; this defines how the individual parts of the linear motors and the guides are assigned to each other in an especially simple way.
An embodiment which enhances the assembly and the ease of processing resides in that the x linear motors are mounted on the rack and the x skid, respectively, by screws that extend in z direction; and in that the y linear motors are mounted on the x skid and the y skid, respectively, by screws that extend in z direction.
When the x linear motors are arranged mirror-symmetrically relative to a central x-z plane of the rack; and when the y linear motors are arranged mirror-symmetrically relative to a central y-z plane of the x skid; this defines optimum arrangements of the linear motors.
When the guides and the linear motors are at least in part openly exposed towards the operating side, large portions of the guides and the linear motors are accessible directly from the operating side, requiring only a displacement of the x skid and/or the y skid to an outermost position.
Further characteristics, advantages and details of the invention will become clear from the following description of an exemplary embodiment with reference to the drawings.